How many solar panels do you need to run a mini split?

By the SmartSolarSizer team · Published 20 October 2026

How much electricity does a 12,000 BTU mini split use?

About 7.0 kWh for 8 hours of cooling at its rated output, or 209 kWh over a 30-day month if it ran like that every day. Those figures come from Mitsubishi's MSZ-FS12NA, which draws 870 W at its rated 12,000 BTU and 1,150 W flat out (Mitsubishi). Even the worst case, 8 hours at maximum input, is 9.2 kWh.

Real use is usually lower. The compressor can throttle down to 2,500 BTU, so once a room is comfortable it ticks over well below 870 W. That's the big difference from a fixed-speed window unit, which cycles between full power and off. Here is the same data for the 9,000 and 18,000 BTU models from their submittal sheets:

Sources: Mitsubishi submittals for MSZ-FS09NA, MSZ-FS12NA and MSZ-FS18NA (the 18k model is rated at 17,200 BTU cooling). These are high-efficiency units: the 9,000 BTU model is rated 29.8 SEER2, about twice the US minimum of 13.4–14.3 SEER2 for central systems (Carrier). Cheaper mini splits with lower SEER2 ratings draw more.

Notice how close the maximum sits to the rated input: only about 30–80% higher. An inverter compressor speeds up gradually rather than starting at full power, which is why mini splits are among the easiest cooling loads to put on solar. Using rated watts for every hour the unit runs is therefore a cautious planning figure.

Solar panels for a 9,000, 12,000 or 18,000 BTU mini split

In Houston, 1 kW of panels makes 3.84 kWh on an average day, so a 430 W panel gives 1.65 kWh. The 12,000 BTU unit's 7.0 kWh takes 5 panels. July is a little sunnier there (4.07 kWh per kW), and it's the month you'd cool most, so the average-day count carries some slack.

All 14 locations for the 12,000 BTU unit cooling 8 hours a day (7.0 kWh), with the hottest month in the last column. For Florida or anywhere else not listed, choose "Somewhere else" in the estimator above and enter your local peak sun hours.

Heating season: why winter needs more panels

A mini split is a heat pump, and a very efficient heater. At full output the 12,000 BTU model delivers 4.24 units of heat for each unit of electricity at 47 °F (8 °C). At 17 °F (−8 °C) that falls to 2.74, and its heat output at the rated point drops to 8,400 BTU. The bigger problem for solar is timing: you want heat in the months when panels make least. In London, 1 kW of panels makes 1.24 kWh a day in December against 2.80 kWh on an average day.

Heating 8 hours at 850 W takes 6.8 kWh a day. That's 5 panels in New York on an average day but 6 in its darkest winter month, and 13 in London in December. On a grid-tied home you'd normally size for the yearly total and let summer surplus offset winter use through net metering. Off-grid, either size for December or keep another heat source, because those December figures are for an average day and a run of grey ones is worse. Our page on how many solar panels to run a heat pump covers whole-house heating.

Inverter size: cooling only or heating too

With almost no start-up surge, you size the inverter on the maximum input plus 25% headroom. Heating draws more than cooling at full output, so the answer depends on how you'll use it:

• Cooling only: about 1,500 W for a 9,000 or 12,000 BTU unit and 3,000 W for an 18,000 BTU unit.
• Cooling and heating: about 3,000 W for a 9,000 or 12,000 BTU unit (maximum heating input 1,740–1,980 W) and 5,000 W for an 18,000 BTU unit (up to 4,000 W).

The units above run on 208–230 V, so an off-grid inverter needs a split-phase or 230 V output. Undersizing here is the common mistake: an inverter picked for summer cooling can trip on the first cold morning when the unit runs flat out to warm the room.

Running a mini split overnight on a battery

Eight hours of the 12,000 BTU unit at rated cooling needs about 8.6 kWh of lithium battery, and the 9,000 BTU unit about 5.5 kWh. Heating through the night at the 47 °F rating takes about 8.4 kWh. Treat all three as ceilings. At night the load is lighter and the compressor throttles down, so real use is often well below rated. If you already have solar monitoring, run the unit for a few nights and read the actual kWh before you buy a bigger battery. A mini split also helps here simply by cooling one bedroom instead of the whole house.

Hybrid AC/DC "solar mini splits"

Some mini splits are sold as solar or AC/DC hybrid units. They take DC power from a few panels directly and top up from the grid or a battery when the sun isn't enough. They suit sheds, cabins, garages and single rooms, where a separate inverter and battery would cost more than the AC. For a whole house, a normal high-efficiency mini split on a grid-tied solar system is usually simpler and easier to get serviced, and the panels can power everything else when the AC is off.

24,000 BTU units and multi-zone systems

We haven't listed a 24,000 BTU mini split because we only use figures from submittal sheets we can link to. Take the rated and maximum input watts from your model's sheet and use the same sums: rated watts × hours for the panels, and maximum input × 1.25 for the inverter (the heating maximum if you'll heat with it).

A multi-zone system has one outdoor unit serving several indoor heads. Size it from the outdoor unit's own spec sheet, because its rated and maximum input already cover all the heads. Separate single-zone units, like the ones above, are easier to plan for: you can add them up room by room in the calculator.

Common questions

Sources

Solar output for every location comes from the European Commission's PVGIS 5.3 (1 kW system, panels at the best fixed angle facing the equator, 14% system losses), retrieved 20 October 2026. Panel counts assume 430 W panels, the most common size in 2025 home solar quotes (EnergySage).

• Mitsubishi MSZ-FS09NA / MUZ-FS09NA submittal
• Mitsubishi MSZ-FS12NA / MUZ-FS12NA submittal
• Mitsubishi MSZ-FS18NA submittal
• Carrier: US minimum efficiency standards (SEER2)

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